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United States Patent |
5,756,587
|
Bettonville
,   et al.
|
May 26, 1998
|
Propylene polymers and process for the production thereof
Abstract
Propylene block copolymer containing per:
100 parts by weight of a polymer (a) of propylene chosen from homopolymers
and copolymers of propylene not containing more than 6% by weight of
ethylene and/or of an alpha-olefin having from 4 to 6 carbon atoms,
from 1 to 100 parts by weight of a polymer (b) of ethylene chosen from
homopolymers and copolymers of ethylene not containing more than 90% by
weight of propylene and/or of another alpha-olefin having from 4 to 6
carbon atoms,
the said block copolymer additionally containing from approximately 0.001
to approximately 20% by weight of .alpha.,.omega.-diene-derived monomer
units with respect to the total weight of the block copolymer.
Inventors:
|
Bettonville; Serge (Crisnee, BE);
De Rop; Philippe (Wavre, BE);
Franquinet; Claude (Brussels, BE)
|
Assignee:
|
Solvay Polyolefins Europe -- Belgium (Societe Anonyme (Brussels, BE)
|
Appl. No.:
|
704509 |
Filed:
|
September 12, 1996 |
PCT Filed:
|
March 7, 1995
|
PCT NO:
|
PCT/EP95/00851
|
371 Date:
|
September 12, 1996
|
102(e) Date:
|
September 12, 1996
|
PCT PUB.NO.:
|
WO95/25137 |
PCT PUB. Date:
|
September 21, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
525/323; 525/268; 525/314 |
Intern'l Class: |
C08F 297/08 |
Field of Search: |
525/268,314,323
|
References Cited
U.S. Patent Documents
4210736 | Jul., 1980 | Baekelmans et al.
| |
4210738 | Jul., 1980 | Hermans et al.
| |
4987193 | Jan., 1991 | Gotoh | 525/313.
|
5206198 | Apr., 1993 | Costa et al.
| |
5438100 | Aug., 1995 | Shinozaki et al. | 525/240.
|
Foreign Patent Documents |
0202946 | Nov., 1986 | EP.
| |
0401993 | Dec., 1990 | EP.
| |
0482855 | Apr., 1992 | EP.
| |
0536503 | Apr., 1993 | EP.
| |
87/6968 | Sep., 1987 | ZA.
| |
Other References
Derwent Abstracts, Abstract No. 84-254528.
Chemical Abstracts, Abstract No. 125417p, vol. 71, No. 13, Dec. 29, 1969.
|
Primary Examiner: Nagumo; Mark
Attorney, Agent or Firm: Spencer & Frank
Claims
What is claimed is:
1. A propylene block copolymer, comprising:
(a) 100 parts by weight of a polymer (a) of propylene selected from
homopolymers and copolymers of propylene not containing more than 60 by
weight of ethylene and/or of an alpha-olefin having from 4 to 6 carbon
atoms, and
(b) from 1 to 100 parts by weight of a polymer (b) of ethylene selected
from copolymers of ethylene containing at least 30% and not more than 90%
by weight of propylene, the polymer (b) additionally containing from
approximately 0.001 to approximately 20% by weight, with respect to the
total weight of the block copolymer comprising polymer (A) of propylene
and polymer (B) of ethylene, of .alpha.,.omega.-diene-derived monomer
units.
2. The block copolymer according to claim 1, wherein the
.alpha.,.omega.-diene contains from 6 to 30 carbon atoms.
3. The block copolymer according to claim 2, wherein the
.alpha.,.omega.-diene is selected from the croup consisting of
1,6-heptadiene, 1-7-octadiene, 1,8-nonadiene, 1,9-decadiene,
1,10-undecadiene, 1,11-dodecadiene, 1,12-tridecadiene and
1,13-tetradecadiene.
4. The block copolymer according to claim 3, wherein the
.alpha.,.omega.-diene is 1,9-decadiene.
5. The block copolymer according to claim 1, wherein the concentration of
.alpha.,.omega.-diene-derived monomer units is from 0.02 to 10% by weight
with respect to the total weight of the block copolymer comprising polymer
(A) of propylene and polymer (B) of ethylene.
6. The block copolymer according to claim 1, comprising:
100 parts by weight of a homopolymer of propylene, and
from 10 to 80 parts by weight of an ethylene copolymer containing from 40
to 60% by weight of propylene and in addition from approximately 0.02 to
approximately 5% by weight with respect to polymer (b) of monomer units
derived from an .alpha.,.omega.-diene.
7. The block copolymer according to claim 1 wherein said copolymer exhibits
stress hardening.
8. The block copolymer according to claim 1 exhibiting an MFI of less than
1 g/10 min.
9. In a process for the production of shaped articles by extrusion
blow-moulding or injection blow-moulding the improvement comprising so
moulding a block copolymer according to claim 1.
10. In process for the production of shaped articles by thermoforming or
coating articles, the improvement comprising thermoforming or coating
articles with a block copolymer according to claim 1.
11. In a process for the formation of foams, the improvement comprising
forming a block copolymer according to claim 1.
12. Block copolymer according to claim 1 exhibiting compatibility between
the polymers (a) and (b).
13. A process for the production of a block copolymer comprising at least
two successive polymerization stages in which a mixture of monomers is
contacted with a catalytic system, under polymerizing conditions,
comprising in a first stage, a mixture of monomer containing:
from approximately 45 to 100% by weight of propylene and which can in
addition contain
up to approximately 5% by weight of ethylene and/or of an alpha-olefin
having from 4 to 6 carbon atoms and
up to approximately 50% by weight of .alpha.,.omega.-diene; and,
in a second stage, a mixture of ethylene, of propylene and of
.alpha.,.omega.-diene containing ethylene and:
up to approximately 90% by weight of propylene and
up to approximately 50% by weight of .alpha.,.omega.-diene, the minimum
amount of .alpha.,.omega.-diene being at least 0.005% by weight.
14. The process according to claim 13, applied to the production of a
propylene block copolymer comprising:
(a) 100 parts by weight of a polymer (a) of propylene selected from
homopolymers and copolymers of propylene not containing more than 6% by
weight of ethylene and/or of an alpha-olefin having from 4 to 6 carbon
atoms, and
(b) from 1 to 100 parts by weight of a polymer (b) of ethylene selected
from copolymers of ethylene containing at least 30% and not more than 90%
by weight of propylene, the polymer (b) additionally containing from
approximately 0.001 to approximately 20% by weight, with respect to the
total weight of the block copolymer comprising polymer (A) of propylene
and polymer (B) of ethylene, of .alpha.,.omega.-diene-derived monomer
units.
15. Process according to claim 13, in which the .alpha.,.omega.-diene is
used only in the second stage.
16. Process according to claim 13, in which the polymerization is carried
out in suspension in an aliphatic hydrocarbon.
17. The process according to claim 16, in which the amounts of the monomers
used are such that:
in the first stage, the ratio of the molar fractions of ethylene and of
propylene in the liquid phase is less than or equal to approximately 0.015
and the ratio of the molar fractions of .alpha.,.omega.-diene and of
propylene in the liquid phase is less than or equal to approximately 5 and
in the second stage, the ratio of the molar fractions of ethylene and of
propylene in the liquid phase is greater than or equal to approximately
0.06 and less than or equal to approximately 0.14 and the ratio of the
molar fractions of .alpha.,.omega.-diene and of propylene in the liquid
phase is less than or equal to approximately 5.
18. The process according to claim 17, in which exclusively propylene is
used in the first stage.
19. The process according to claim 13, in which the polymerization is
carried out by means of a catalytic system containing a complexed solid
comprising TiCl.sub.3 and an activator chosen from organoaluminium
compounds.
20. The process according to claim 19, in which the complexed catalytic
solid comprising TiCl.sub.3 has been subjected to a prepolymerization
treatment so as to incorporate therein at least 50% by weight of polymer
with respect to the weight of TiCl.sub.3.
Description
FIELD OF THE INVENTION
The present invention relates to propylene block copolymers containing a
non-conjugated .alpha.,.omega.-diene. It more particularly relates to
propylene block copolymers containing a non-conjugated
.alpha.,.omega.-diene in at least one of the blocks and to a process for
the production of these copolymers.
TECHNOLOGY REVIEW
It is known to increase the impact strength of polypropylene by mixing it
with ethylene-propylene elastomers. Nevertheless, as such mixtures are not
perfectly homogeneous, they do not exhibit all the desired properties.
Attempts have been made to overcome this problem by copolymerizing
propylene with another alpha-olefin, such as, for example, ethylene.
Among propylene copolymers, those which exhibit the best impact
strength/stiffness compromise are the copolymers, known as block
copolymers, prepared in two-stage processes comprising a first stage of
homopolymerization of the propylene or of copolymerization of the
propylene with a maximum of 6 molar % of another alpha-olefin, such as
ethylene, followed by a second stage of polymerization of ethylene or of
copolymerization of ethylene with propylene and optionally another
alpha-olefin in proportions such that the amount of ethylene is greater
than 10 molar % (see, for example, EP-0,202,946).
The rheological properties of these block copolymers and in particular
their melt strength remain unsatisfactory however for specific
applications, such as thermoforming or the production of foams.
In addition, when the block copolymers are obtained by polymerization in a
diluent, such as a hydrocarbon or one of the monomers maintained in the
liquid state, the formation of a significant amount of diluent-soluble
polymer is observed in the second polymerization stage, which results in
an increase in the viscosity of the polymerization mixture, a
deterioration in heat exchanges and agglomeration of the polymer particles
with each other or on the walls of the reactor. Under these conditions, it
is necessary to limit the amount of polymer produced during this stage,
which results in a limitation on the impact strength of the final
copolymers. The loss of polymer by solubilization is also responsible for
a substantial increase in production costs.
Moreover, the document JP 59/155416 discloses propylene block copolymers in
which each of the blocks contains from 1 to 30% by weight of 4- or
5-methyl-1,4-hexadiene. These copolymers exhibit good impact strength and
are chemically reactive.
SUMMARY OF THE INVENTION
The present invention relates to propylene block copolymers which are
different from those described in the prior art and which exhibit many
advantages with respect to the latter.
To this end, the present invention relates to a propylene block copolymer
containing per:
100 parts by weight of a polymer (a) of propylene chosen from homopolymers
and copolymers of propylene not containing more than 6% by weight of
ethylene and/or of an alpha-olefin having from 4 to 6 carbon atoms,
from 1 to 100 parts by weight of a polymer (b) of ethylene chosen from
homopolymers and copolymers of ethylene not containing more than 90% by
weight of propylene and/or of another alpha-olefin having from 4 to 6
carbon atoms,
the said block copolymer additionally containing from approximately 0.001
to approximately 20% by weight of .alpha.,.omega.-diene-derived monomer
units with respect to the total weight of the block copolymer.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE illustrates the variation in the elongational viscosity in the
molten state (expressed in Pa.s) as a function of the elongation time
(expressed in s) for elongation rate gradients of 0.1 s.sup.-1.
DETAILED DESCRIPTION OF THE INVENTION
The propylene block copolymers according to the present invention most
often contain at least 5 parts by weight and preferably at least 10 parts
by weight of polymer (b) per 100 parts by weight of polymer (a). The
copolymers according to the invention which contain at least 20 parts by
weight of polymer (b) per 100 parts by weight of polymer (a) give good
results. The amount of polymer (b) is in addition not generally greater
than 90 parts by weight. Good results are obtained when the amount of
polymer (b) is less than or equal to 80 parts by weight per 100 parts of
polymer (a).
The polymer (a) is generally a homopolymer of propylene or a copolymer of
propylene and of ethylene not containing more than 3% by weight of
ethylene. Good results are obtained when the polymer (a) is a homopolymer
of propylene.
The polymer (b) is generally a copolymer of ethylene. It is most often a
copolymer of ethylene containing at least 30%, preferably at least 40%, by
weight of propylene. The propylene concentration in the polymer (b) is in
addition generally less than or equal to 70% by weight, more particularly
less than or equal to 60% by weight.
The block copolymers according to the present invention contain, in
addition to the monomer units derived from propylene, from ethylene and
optionally from an alpha-olefin, from approximately 0.001 to approximately
20% by weight of monomer units derived from an .alpha.,.omega.-diene with
respect to the total weight of the block copolymer.
.alpha.,.omega.-Dienes denote diolefins containing two end carbon-carbon
double bonds. The .alpha.,.omega.-dienes which can be used in the block
copolymers according to the invention generally contain from 6 to 30
carbon atoms. The preferred .alpha.,.omega.-dienes contain at least 7
carbon atoms. Most often, they do not contain more than 15 carbon atoms.
Mention may be made, as examples of these compounds, of 1,6-heptadiene,
1,7-octadiene, 1,8-nonadiene, 1,9-decadiene, 1,10-undecadiene,
1,11-dodecadiene, 1,12-tridecadiene and 1,13-tetradecadiene. Among these
compounds, 1,7-octadiene, 1,8-nonadiene and 1,9-decadiene give good
results. 1,9-Decadiene is more particularly preferred.
It is obvious that the block copolymers according to the invention which
contain monomer units derived from one or from a number of
.alpha.,.omega.-dienes also come within the scope of the present
invention.
The concentration of .alpha.,.omega.-diene-derived monomer units in the
block copolymers according to the present invention is generally greater
than or equal to approximately 0.01% by weight with respect to the total
weight of the block copolymer. This concentration is preferably greater
than or equal to approximately 0.02% by weight with respect to the total
weight of the block copolymer. Most often, the concentration of
.alpha.,.omega.-diene-derived monomer units is less than or equal to
approximately 10% by weight with respect to the total weight of the block
copolymer. Good results are obtained when it is not greater than
approximately 5% by weight with respect to the total weight of the block
copolymer. The block copolymers in which the concentration of
.alpha.,.omega.-diene-derived monomer units is from 0.02 to 10% by weight
with respect to their total weight are highly suitable.
The preferred block copolymers are generally such that the
.alpha.,.omega.-diene-derived monomer units are present solely in the
polymer (b).
Consequently, the propylene block copolymers according to the present
invention most often contain per:
100 parts by weight of a polymer (a) of propylene chosen from homopolymers
and copolymers of propylene not containing more than 6% by weight of
ethylene and/or of an alpha-olefin having from 4 to 6 carbon atoms,
from 1 to 100 parts by weight of a polymer (b) of ethylene chosen from
ethylene copolymers containing at least 30% and not more than 70% by
weight of propylene and additionally containing from approximately 0.001
to approximately 20% by weight of .alpha.,.omega.diene-derived monomer
units with respect to the total weight of the block copolymer.
Very particularly preferred block copolymers contain per:
100 parts by weight of a polymer (a) which is a homopolymer of propylene,
from 10 to 80 parts by weight of a polymer (b) which is an ethylene
copolymer containing from 40 to 60% by weight of propylene and in addition
from approximately 0.02 to approximately 5% by weight of monomer units
derived from an .alpha.,.omega.-diene.
The block copolymers according to the present invention possess the usual
properties of block copolymers, such as a good stiffness/impact strength
compromise, good impact strength at low temperature, and the like. The
stiffness/impact strength compromise of the block copolymers according to
the invention is generally superior to that of the block copolymers in
which the first block is a propylene homopolymer and in which the second
block is a propylene-ethylene elastomer.
They in addition exhibit, due to the presence of monomer units derived from
the .alpha.,.omega.-diene, a relatively large number of branchings which
confers on them a good melt strength characterized by a high elongational
viscosity at low rate gradient.
These block copolymers also exhibit, in the molten state, an increase in
the resistance to deformation during elongation or extension. Such a
phenomenon is generally known as "stress hardening". It can easily be
characterized by determining, for a given temperature and a given
elongation rate, the variation in the elongational viscosity of the block
copolymer in the molten state as a function of the elongation time. When
subjected to such tests, the block copolymers according to the present
invention exhibit an increase in the elongational viscosity until the
molten polymer mass ruptures, this rupture generally being brittle.
When subjected to these same tests, the block copolymers of the prior art
do not exhibit such a phenomenon.
These different properties make the block copolymers according to the
present invention particularly suitable for being shaped by extrusion or
by injection and in particular by extrusion blow-moulding or injection
blow-moulding. These block copolymers are also suitable for being used by
thermoforming or coating. They are also highly suitable for the formation
of foams.
The block copolymers according to the present invention in addition exhibit
a wide range of melt flow indices (MFI, measured according to ASTM
standard D 1238 (1986)) and can exhibit smaller MFI values than those
usually encountered for the block copolymers of the prior art. For this
reason, the block copolymers according to the present invention which
exhibit an MFI of less than 1 g/10 min, in particular of less than 0.7 and
more particularly of less than 0.4 g/10 min, constitute an additional
aspect of the invention. These specific block copolymers are particularly
well suited to applications requiring very good melt strength, as
described above.
Finally, the block copolymers according to the present invention generally
also exhibit unsaturations arising from the incorporation, in the polymer
chains, of the .alpha.,.omega.-diene-derived units. These unsaturations
make it possible to graft polar monomers, such as, as non-limiting
example, maleic anhydride, without significant degradation of the polymer.
It is thus possible to improve the printability properties of the block
copolymers, their adhesion to different substrates and the adhesion of
paint on the articles obtained from these block copolymers. These
unsaturations can also be used to obtain, by appropriate means, good
compatibility between the polymers (a) and (b) constituting the block
copolymer.
Such uses consequently also constitute additional aspects of the present
invention.
The present invention also relates to a process for producing these block
copolymers. The block copolymers according to the present invention are
generally obtained according to a process comprising at least two
successive polymerization stages during which the polymers (a) and (b) are
respectively formed.
The process according to the present invention consequently comprises at
least two successive polymerization stages in which use is made, under
polymerizing conditions, in the presence of a catalytic system, of
mixtures of monomers containing:
in the first stage, propylene and optionally up to approximately 5% by
weight of ethylene and/or of an alpha-olefin having from 4 to 6 carbon
atoms and/or up to approximately 50% by weight of .alpha.,.omega.-diene
with respect to the combined monomers used in this stage, and
in the second stage, ethylene and optionally up to 95% by weight of
propylene and/or of another alpha-olefin having from 4 to 6 carbon atoms
and/or up to approximately 50% by weight of .alpha.,.omega.-diene with
respect to the combined monomers used in this stage, at least one of these
two stages being carried out while making use of a mixture of monomers
containing at least 0.005% by weight of .alpha.,.omega.-diene.
The minimum amount of .alpha.,.omega.-diene used in at least one of these
two stages is generally approximately 0.01% by weight and more
particularly approximately 0.1% by weight.
The amount of .alpha.,.omega.-diene used in at least one of these two
stages generally does not exceed 30% by weight and more particularly does
not exceed 20% by weight of the mixture of monomers used in this or these
stages.
Generally, the .alpha.,.omega.-diene is used at least in the second
polymerization stage. Processes giving good results are such that use is
made, as monomers, of:
in the first stage, propylene which can optionally contain up to
approximately 5% by weight of ethylene and/or of an alpha-olefin having
from 4 to 6 carbon atoms and/or up to approximately 50% by weight of
.alpha.,.omega.-diene with respect to the combined monomers used, and
in the second stage, a mixture of ethylene, of propylene and of
.alpha.,.omega.-diene containing up to approximately 90% by weight of
propylene and up to approximately 50% by weight of .alpha.,.omega.-diene
with respect to the combined monomers used in this stage.
The amount of propylene used in this second stage is in addition most often
at least approximately 50% by weight and more particularly at least
approximately 80% by weight.
The .alpha.,.omega.-diene is preferably used exclusively in the second
polymerization stage.
The process according to the present invention is generally carried out so
that, in the second stage, from 1 to 100 parts by weight of polymer are
formed per 100 parts by weight of polymer formed in the first stage.
The first and the second stage are in addition most often carried out under
conditions such that the respective amounts of polymer formed are those
described above with respect to the polymers (a) and (b) of the block
copolymers according to the invention.
The two polymerization stages of the process according to the invention can
be carried out successively in the same reactor. The second stage is then
carried out in the presence of the polymer formed in the first stage and
after having completely or partially removed the unreacted monomers. These
two stages can also be carried out in two reactors arranged in series. The
second stage is then carried out in the second reactor in the presence of
the polymer formed in the first stage and after having completely or
partially removed the unreacted monomers arising from the first reactor.
The polymerization process according to the present invention is
advantageously carried out in two reactors in series.
The first stage of the process according to the present invention is
generally carried out in the absence of alpha-olefin having 4 to 6 carbon
atoms. In addition, good results are obtained when use is not made of
ethylene when this stage is carried out.
The first stage of the process according to the invention is preferably a
stage of homopolymerization of propylene.
The monomers used during the second stage are generally ethylene, propylene
and the .alpha.,.omega.-diene. Moreover, good results are obtained when
the respective amounts of ethylene and of propylene used are such that the
ratio by weight of these monomers in the polymer formed during this stage
is greater than or equal to 0.4 and more particularly greater than or
equal to 0.65. In addition, these amounts are most often such that the
ratio by weight of these monomers in the polymer formed during this stage
is less than or equal to 2.4, preferably less than or equal to 1.5.
The amount of .alpha.,.omega.-diene used in the process according to the
invention is generally such that the overall composition of the block
copolymer which is formed therein is that described above with respect to
the block copolymers according to the invention.
In the processes according to the present invention, the polymerization can
be carried out according to any known process. This polymerization can be
carried out in solution or in suspension in an inert hydrocarbon diluent
generally chosen from liquid aliphatic, cycloaliphatic and aromatic
hydrocarbons such as, for example, liquid alkanes and isoalkanes, benzene
and its derivatives. Hydrocarbon diluents preferentially used are: butane,
isobutane, hexane, heptane, cyclohexane, methylcyclohexane or their
mixtures. Hexane and heptane are highly suitable. It is also possible to
carry out the polymerization in the monomer or in one of the monomers
maintained in the liquid state or alternatively in the gas phase.
It is also possible to carry out the first and the second stage according
to two different processes.
Advantageously, at least the second stage is carried out in suspension in a
hydrocarbon solvent such as described above.
The polymerization temperature is generally chosen from 20.degree. to
200.degree. C. and preferably from 50.degree. to 90.degree. C. The
pressure is most often chosen between atmospheric pressure and 50
atmospheres. The temperature and the pressure are, of course, a function
of one another and of the nature of the polymerization process used.
The preferred process according to the present invention comprises two
polymerization stages carried out in suspension in a hydrocarbon solvent.
In this specific case, the amounts of monomers used in the first stage are
such that the ratio of the molar fractions of ethylene and of propylene in
the liquid phase is less than or equal to approximately 0.015 and the
ratio of the molar fractions of .alpha.,.omega.diene and of propylene in
the liquid phase is less than or equal to approximately 5.
Moreover, the amounts of monomers used in the second stage are such that
the ratio of the molar fractions of ethylene and of propylene in the
liquid phase is greater than or equal to approximately 0.06 and less than
or equal to approximately 0.14 and the ratio of the molar fractions of
.alpha.,.omega.-diene and of propylene in the liquid phase is less than or
equal to 5.
Good results are obtained when the amounts of monomers used for producing
the block copolymers according to the invention are such that:
in the first stage, the ratio of the molar fractions of ethylene and of
propylene in the liquid phase is less than or equal to approximately 0.015
and the ratio of the molar fractions of .alpha.,.omega.-diene and of
propylene in the liquid phase is less than or equal to approximately 5,
and
in the second stage, the ratio of the molar fractions of ethylene and of
propylene in the liquid phase is greater than or equal to approximately
0.06 and less than or equal to approximately 0.14 and the ratio of the
molar fractions of .alpha.,.omega.-diene and of propylene in the liquid
phase is less than or equal to approximately 5.
In the first stage, the ratio of the molar fractions of ethylene and of
propylene in the liquid phase is preferably less than or equal to
approximately 0.006. When use is made of an .alpha.,.omega.-diene in the
first stage, the amounts of monomers used are most often such that the
ratio of the molar fractions of .alpha.,.omega.-diene and of propylene in
the liquid phase is less than or equal to approximately 2.5 and more
particularly less than or equal to approximately 1.5. Preferably, ethylene
is not used. Good results are obtained when .alpha.,.omega.-diene is not
used in the first stage. The best results are obtained when exclusively
propylene is used in the first stage.
In the second stage, the ratio of the molar fractions of ethylene and of
propylene in the liquid phase is preferably less than or equal to
approximately 0.12. In addition, it is most often greater than or equal to
approximately 0.08. The amounts of .alpha.,.omega.-diene used in this
second stage are most often such that the ratio of the molar fractions of
.alpha.,.omega.-diene and of propylene in the liquid phase is less than or
equal to approximately 2.5, more particularly less than or equal to
approximately 1.5. In addition, this ratio is generally at least
2.times.10.sup.-4, most often at least 2.times.10.sup.-3 and preferably at
least 5.times.10.sup.-3.
When the polymerization is carried out in a hydrocarbon diluent, it is
noticed, surprisingly, that the presence of the .alpha.,.omega.-diene
results in a decrease in the amount of polymer soluble in the
polymerization mixture. Such behaviour is particularly advantageous during
the production of the polymer (b). In fact, it makes possible greater
incorporation of the elastomer block in the final block copolymer, without
problems of adhesion of the polymer particles to one another and/or on the
walls of the reactor being observed. Block copolymers are thus easily
obtained, containing a greater proportion of elastomer fraction, which
possess a particularly high impact strength. Such a phenomenon is also
observed when the polymerization is carried out in one of the monomers
maintained in the liquid state.
Moreover, at a constant content of polymer (b), the block copolymers which
contain an .alpha.,.omega.-diene are obtained with a better economical
yield and exhibit a better morphology.
The catalytic systems which can be used in the processes according to the
present invention generally comprise a catalytic solid comprising at least
one transition metal belonging to the group IVb of the Periodic Table and
an activator generally chosen from organoaluminium compounds.
These catalytic systems are well known to the person skilled in the art.
The preferred catalytic systems according to the present invention contain,
as catalytic solid, a complexed solid based on titanium trichloride
(TiCl.sub.3) as described, for example, in United States Patents U.S. Pat.
No. 4,210,738, U.S. Pat. No. 4,210,736 and U.S. Pat. No. 5,206,198
(Solvay) and in Patent Application EP-A-261,727 (Solvay), the contents of
which are incorporated by reference in the present description. It proves
to be advantageous, in order to obtain block copolymers exhibiting a
particularly beautiful morphology, to use catalytic solids which have in
addition been subjected to a prepolymerization treatment which comprises
bringing them into contact with an alpha-olefin, such as, preferably,
propylene or ethylene, under polymerizing conditions, so as to obtain
solids containing at least 50% by weight of polymer with respect to the
weight of titanium chloride. The maximum amount of prepolymer is not
critical. For economical reasons, it is preferable for it not to be
greater than 2000% by weight with respect to the TiCl.sub.3. The amount of
polymer produced during this stage is preferably greater than 100 g per kg
of TiCl.sub.3. Amounts of prepolymer of less than 1000 g per kg of
TiCl.sub.3 give satisfactory results. The prepolymerization is generally
carried out at the end of the preparation of the catalytic solid. It can
also be carried out in a polymerization stage directly preceding the
stages of production of the polymers (a) and (b).
The organoaluminium activator is generally chosen from the compounds
corresponding to the formula:
AlR.sup.1.sub.n X.sub.3-n
in which
R.sup.1 is a hydrocarbon radical containing from 1 to 18 carbon atoms;
X is a halogen; and
n is a number such that 0<n.ltoreq.3.
Surprisingly, it is found that, when the catalytic solid is a solid based
on TiCl.sub.3, the properties of the block copolymers depend on the nature
of the catalytic system used in their production and in particular on the
nature of the organoaluminium activator.
Thus, generally, the use of a halogenated organoaluminium activator results
in block copolymers preferentially exhibiting branched polymer chains
which confer on them the advantageous rheological properties also
described above.
Moreover, the use of a non-halogenated organoaluminium activator, such as,
for example, a trialkylaluminium, in addition promotes the presence of
unsaturations in the polymer chains which gives rise, optionally after
chemical conversion, to the adhesion and printability properties described
above.
For this reason, the production process according to the present invention
has the advantage of being able, by simple modification of the nature of
the activator, to result in the production of block copolymers exhibiting
different properties.
The catalytic systems which can be used for the production of the block
copolymers according to the present invention can also contain at least
one third constituent known for improving their stereospecificity and/or
their activity.
The various constituents of the catalytic systems which can be used in the
processes according to the present invention are generally all introduced
during the first polymerization stage.
The total amount of the various constituents of the catalytic systems which
can be used according to the present invention is not critical and forms
part of what is generally known to a person skilled in the art. The total
amount of activator used is generally greater than 0.1 mmol per liter of
diluent, of liquid monomer or of reactor volume, preferably greater than
0.5 mmol per liter. When the catalytic solid is a catalytic solid based on
TiCl.sub.3, the amount of catalytic solid used is determined as a function
of its TiCl.sub.3 content. It is most often chosen so that the
concentration of TiCl.sub.3 in the polymerization mixture is greater than
0.01 mmol per liter of diluent, of liquid monomer or of reactor volume and
preferably greater than 0.05 mmol per liter. The ratio of the amount of
organoaluminium compound to the amount of catalytic solid based on
TiCl.sub.3 is generally chosen so that the molar ratio of the activator to
the TiCl.sub.3 is between 0.5 and 20, preferably between 1 and 15. The
best results are obtained when the molar ratio is between 2 and 12.
The average molecular mass of the block copolymers according to the present
invention can be adjusted by the addition to the polymerization mixture of
one or a number of agents for adjusting the average molecular mass, such
as hydrogen, diethylzinc, alcohols, ethers and alkyl halides. Hydrogen is
particularly well suited.
EXAMPLES
The following examples serve to illustrate the invention. The elongational
viscosity of the block copolymers obtained in these examples is determined
by means of a rheometer marketed by Rheometrics under the name Rheometrics
Extensional Rheometer RER-9000. The curves of the variation in the
elongational viscosity in the molten state (expressed in Pa.s) as a
function of the elongation time (expressed in s) for elongation rate
gradients of 0.1 s.sup.-1 are reproduced in the single appended figure.
These curves were recorded at 190.degree. C. The curve 1R relates to
Example 1R and the curves 2 and 3 relate respectively to Examples 2 and 3.
The meaning of the symbols used in these examples, the units expressing
the quantities mentioned and the methods for measuring these quantities
are explained below.
prod=Catalytic productivity expressed conventionally in grams of polymer
obtained per gram of TiCl.sub.3 contained in the catalytic solid. This
activity is assessed indirectly from the determination of the residual
titanium content in the polymer by X-ray fluorescence.
Sol=Amount of polymer soluble in the polymerization mixture expressed as %
by weight with respect to the total amount of polymer collected.
AD=Apparent density of the insoluble polymer expressed in g/dm.sup.3.
MFI=Melt flow index measured under a load of 2.16 kg at 230.degree. C. and
expressed in g/10 min (ASTM standard D 1238 (1986)).
Flex. Mod.=Flexural modulus of the block copolymers measured according to
ISO standard 178 (1993) expressed in MPa.
g=Torsional stiffness modulus of the block copolymers, measured at
100.degree. C. and for an angle of torsion of 60.degree. C. of arc, the
temperature of the mould being set at 70.degree. C. and the duration of
conditioning at 5 minutes (ASTM standard D 1043 (1987)). This modulus is
expressed in daN/cm.sup.2.
Izod=Measurement of the resilience of the polymers, expressed in
kJ/m.sup.2, measured according to ISO standard 180/1A (1993).
Embrit. Temp.=Embrittlement temperature of the polymers measured according
to ASTM standard D 746, expressed in .degree. C.
EXAMPLE 1R
This example is given by way of reference. It illustrates the block
copolymers not containing .alpha.,.omega.-diene.
A--Preparation of the Catalytic Solid
90 ml of hexane and 60 ml of TiCl.sub.4 are introduced, under a nitrogen
atmosphere and with stirring, into an 800 ml reactor. This
hexane/TiCl.sub.4 solution is cooled to 0 (.+-.1).degree. C. and a
solution composed of 190 ml of hexane and of 70 ml of diethylaluminium
chloride (DEAC) is added thereto over 4 hours, a temperature of 0.degree.
C. being maintained in the reactor.
The reaction mixture, composed of a suspension of fine particles, is then
kept stirring at this temperature for 15 min, is then brought over 1 hour
to 25.degree. C. and maintained for 1 hour at this temperature before
being brought over approximately 1 hour to 65.degree. C. The mixture is
kept stirring for 2 hours at 65.degree. C., is then cooled to
approximately 55.degree. C. and propylene is introduced, into the gaseous
head space of the reactor, under a pressure of 2 bars. This introduction
is continued for a time (approximately 45 min) sufficient to obtain, per
kg of final solid, 65 g of polymerized propylene. The suspension of the
thus prepolymerized solid is then cooled to 40.degree. C. and washed with
hexane.
The reduced solid is then suspended in 456 ml of hexane and 86 ml of
diisoamyl ether (DIAE) are added thereto. The suspension is stirred at 250
rev/min for 1 hour at 50.degree. C. and then separated by settling. After
having removed the supernatant, the solid is resuspended in 210 ml of
hexane and 52 ml of TiCl.sub.4 are added thereto. The suspension is then
kept stirring (150 rev/min) at 75.degree. C. for 2 hours. After washing,
the complexed solid based on TiCl.sub.3 is resuspended in hexane (in the
proportion of 4 ml of hexane per gram of solid) and brought into contact
with 120 ml of a solution containing, per liter of hexane, 80 g of DEAC
and 176 g of n-octadecyl
3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate.
On completion of addition, the suspension is kept stirring for 1 hour at
30.degree. C. before introducing propylene under a pressure of 2 bars for
a time (approximately 30 min) sufficient to obtain 170 g of PP per kg of
final dry product.
The catalytic solid contains, after washing and drying, 630 g of TiCl.sub.3
per kg.
B. Preparation of the Block Copolymer
The following are introduced, under a dry nitrogen flow, into a predried 5
l autoclave:
1.5 liters of hexane,
700 mg of DEAC,
20 mg of ethyl benzoate.
The autoclave is then heated to 60.degree. C. and repressurized with
propylene to atmospheric pressure before successively introducing therein
a hydrogen pressure of 1 bar, a propylene pressure of 4 bars and an amount
of catalytic solid as described in part A sufficient for the amount of
TiCl.sub.3 introduced into the reactor to be approximately 120 mg.
The reactor is maintained at 60.degree. C. for 3 hours while supplying it
with propylene so as to keep the pressure in the reactor constant.
Under these conditions, the molar fraction of propylene in the liquid phase
is 0.25.
After polymerizing for 3 hours, the temperature of the autoclave is brought
to 45.degree. C. while degassing it to a pressure of 3 bars.
Approximately 0.03 bar of hydrogen is then introduced and the pressure is
adjusted, by means of propylene, to 3.1 bars and then, by addition of
ethylene, to 4.6 bars.
The polymer (b) is obtained by polymerizing under these conditions for 1
hour and by keeping the composition of the gaseous phase constant.
The molar fraction of ethylene in the liquid phase is 0.028 and that of
propylene is 0.253.
A block copolymer is thus obtained, with a productivity prod of 3653, which
exhibits the following properties:
Sol=3.2
AD=500
MFI=5.4
Ethylene content in the final block copolymer=9% by weight.
Examples 2 to 4
These examples illustrate the production of block copolymers according to
the invention in which the polymer (a) is a homopolymer of propylene and
in which the polymer (b) is an ethylene-propylene copolymer containing an
.alpha.,.omega.-diene: 1,9-decadiene.
The catalytic solid used in carrying out these examples is that of Example
1.
The block copolymer is obtained by repeating the procedure of Example I but
by introducing the .alpha.,.omega.-diene after the degassing of the
autoclave to 3 bars for the preparation of the polymer (b).
The conditions for the production of these block copolymers as well as
their properties are reproduced in Table I.
TABLE I
______________________________________
Examples 2 3 4
______________________________________
Preparation of the Polymer (b)
.alpha.,.omega.-Diene used (ml)
5 10 50
Molar fraction of ethylene in
0.028 -- 0.028
the liquid phase
Molar fraction of propylene in
0.253 -- 0.253
the liquid phase
Molar fraction of .alpha.,.omega.-diene in
1.5 .times. 10.sup.3
-- 0.015
the liquid phase
Polymerization results
prod 3653 3741 3787
Amount of polymer (b)
18 18 18
Amount of polymer (a)
82 82 82
Sol 1.7 1.4 1.2
AD 507 507 508
MFI 1 0.9 0.2
Ethylene content in the final
6 6 6
block copolymer (% by weight)
______________________________________
Comparison of these results with those of Example 1 given by way of
reference enables the low level of soluble material observed when the
polymerization is carried out in the presence of .alpha.,.omega.-diene, as
well as the good morphology of the block copolymers obtained, to be
demonstrated.
Examination of the curves reproduced in the single figure clearly shows
that the block copolymers according to the present invention exhibit the
phenomenon of stress hardening.
Example 5
Example 2 is repeated, except as regards the polymerization time for the
stage for formation of the polymer (b) (1.5 hours) and as regards the
amount of .alpha.,.omega.-diene used (20 ml).
The properties of the block copolymer obtained are:
prod=3833; Amount of polymer (a)=73; Amount of polymer (b)=27; Sol=2.2;
AD=489; MFI=0.2; Ethylene content in the final block copolymer=12% by
weight.
Example 6R
Example 5 is repeated, the introduction of the .alpha.,.omega.-diene being
omitted.
The properties of the block copolymer obtained are:
prod=3833; Amount of polymer (a)=73; Amount of polymer (b)=27; Sol=4.0;
AD=487; MFI=3.2; Ethylene content in the final block copolymer=12% by
weight.
Reference Example 7R and Example According to the invention 8
A. Preparation of the Catalytic Solid
The catalytic solid is prepared as described in Example 1R, part A but the
final treatment with propylene being omitted.
B. Preparation of the Block Copolymers
Example 7R is carried out by repeating Part B of Example 1R. The block
copolymer according to Example 8 is obtained by repeating Example 2. The
properties of the block copolymers obtained are reproduced in Table II
below.
TABLE II
______________________________________
Examples 7R 8
______________________________________
prod 3339 3450
Amount of polymer (b)
18 18
Amount of polymer (a)
82 82
Sol 3.8 3
AD 486 488
MFI 11.6 1.9
Ethylene content in the
8 8
final block copolymer
Flex. Mod. 1350 1378
g 680 675
Izod 3.7 4.2
Embrit. Temp. -23 -33
______________________________________
Comparison of these results enables the better impact strength/stiffness
compromise of the block copolymers according to the invention to be
demonstrated.
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